The invention relates to a method for controlling free-wheeling in a dual clutch transmission in a vehicle for achieving minimum energy losses and sufficient lubrication of the transmission during free-wheeling.
The invention can be, applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle.
A dual clutch transmission is a transmission with two input shafts where each input shaft has its own clutch and where one of the input shafts is used by one set of gears, for instance odd gears, and the other input shaft is used by a second set of gears, for instance even gears. The clutches connect the input shafts to the provider of mechanical energy in the vehicle, which can be a prime mover such as an internal combustion engine or an electric motor.
Free-wheeling is defined as a state when the vehicle is allowed to roll without driving or braking torque on the wheels. This requires disconnecting the engine from the driving wheels of the vehicle. One problem relating to this operation can include energy losses caused by clutch actuation to achieve said disconnection, where the clutch must be maintained in its actuated position while the vehicle is in free-wheeling mode.
A further problem relates to insufficient lubrication of the transmission caused by deactivation of a clutch connected to a drive shall for driving an oil pump. When a clutch is actuated to initiate free-wheeling mode, this action can simultaneously stop the transmission lubrication pump. Known solutions can involve the provision of an electric motor for driving the lubrication pump during periods of torque interruption.
When the free-wheeling mode is terminated there may also be problems relating to delays in re-connection of the engine to the driving wheels. During a period of torque interruption one or more shafts in the transmission may stop rotating, wherein said shafts must be brought up to speed before re-connection or a gear change can be performed.
It is desirable to provide an improved method and arrangement for controlling a dual clutch transmission during free-wheeling that solves or minimizes the above problems.
It is desirable to provide a method and a device for controlling free-wheeling in a dual clutch transmission in a vehicle, which method and device aims at achieving minimum energy losses and sufficient lubrication of the transmission during free-wheeling.
The provision of a method and a device for controlling free-wheeling in a dual clutch transmission according to an aspect of the invention will give a number of advantages such as low energy losses, as no clutch actuation forces are required during free-wheeling mode. Sufficient lubrication of the transmission during free-wheeling mode is ensured as the lubrication pump is driven via a clutch connected to the output shaft of a prime mover. A further advantage is that fast and safe engagement of the prime mover to the driven wheels after termination of free-wheeling mode is achieved without having to bring the transmission up to speed or to actuate and engage a gear set, as the on-coming gear has already been preselected.
A first embodiment relates to a method for controlling free-wheeling in a dual clutch transmission in a vehicle. The transmission comprises a first transmission mechanism arranged to transmit mechanical driving force from an output shaft of a prime mover, such as an internal combustion engine, to a first input shaft and to put each of a first set of gears in an engaged state to connect the first input shaft to the driving wheels. The transmission further comprises a second transmission mechanism arranged to transmit mechanical driving force from the output shaft of the prime mover to a second input shaft and to put any one of a second set of gears in an engaged state to connect the second input shaft to the driving wheels.
In this context, the term transmission mechanism is defined as comprising the component parts required for transmitting torque between the prime mover and the driven wheels via the first or the second input shaft, including the respective clutches associated with the first and second input shafts, respectively.
The first transmission mechanism comprises a controllable first clutch unit arranged to bring the output shaft of the prime mover and the first input shaft into engagement with each other. Similarly, the second transmission mechanism comprises a controllable second clutch unit arranged to bring the output shaft of the prime mover and the second input shaft into engagement with each other. An electronic control unit is arranged to control gear selection and clutch unit actuation. The control unit is arranged to monitor the dual clutch transmission and to control the transmission in response to input signals from the driver and detected prime mover and transmission parameters.
The invention involves performing the following method steps upon determining that a freewheeling mode is to be initiated:                deactivating the first clutch unit, wherein the output shaft of the prime mover and the first input shaft are engaged;        disengaging each of the first set of gears connecting the first input shaft to the driving wheels.        deactivating the second clutch unit, wherein the output shaft of the prime mover and the second input shaft are disengaged; and        engaging one of the second set of gears connecting the second input shaft to the driving wheels.        
In this example, the first clutch unit is normally closed which means that the clutch is held in a closed, engaged position by a resilient means, a spring or a similar suitable means. To disengage the first clutch it is actuated by fluid pressure or other suitable means. A non-exhaustive list of actuating means includes hydraulic or pneumatic pressure, as well as electromagnetic or electromechanical means. The second clutch unit is normally open which means that the clutch is held in an open, disengaged position by a resilient means, a spring or a similar suitable means. To engage the second clutch it is actuated by hydraulic pressure or other suitable means.
According to the method, a transmission lubricating device is connected to and driven by the first transmission mechanism during a free-wheeling mode. This ensures sufficient lubrication of the transmission during free-wheeling, when no torque is transmitted between the prime mover and the driving wheels.
A method and an arrangement for controlling free-wheeling in a dual clutch transmission in a vehicle, which transmission includes a first and a second transmission mechanism controllable by a first and a second clutch unit, each connected to a first and a second input shaft respectively, involves deactivating the first clutch unit, wherein the output shaft of the internal combustion engine and the first input shaft are engaged, and disengaging each of the first set of gears connecting the first input shaft to the driving wheels. Simultaneously, the second clutch unit is deactivated, wherein the output shaft of the internal combustion engine and the second input shaft are disengaged, and one of the second set of gears connecting the second input shaft to the driving wheels is engaged.
According to a further embodiment, a dual clutch transmission in a vehicle is provided, which transmission comprises a first transmission mechanism arranged to transmit mechanical driving force from an output shaft of the prime mover to a first input shaft and to put each of a first set of gears in an engaged state to connect the first input shaft to the driving wheels. The transmission further comprises a second transmission mechanism arranged to transmit mechanical driving power from the output shaft of the prime mover to a second input shaft and to put one of a second set of gears in an engaged state to connect the second input shaft to the driving wheels. The definition of a “transmission mechanism” has been outlined above.
The first transmission mechanism comprises a controllable first clutch unit arranged to bring the output shaft of the prime mover and the first input shaft into engagement with each other. Similarly, the second transmission mechanism comprises a controllable second clutch unit arranged to bring the output shaft of the prime mover and the second input shaft into engagement with each other. An electronic control unit is arranged to control gear selection and clutch unit actuation. As indicated above, the control unit is arranged to monitor the dual clutch transmission and to control the transmission in response to input signals from the driver and detected prime mover and transmission parameters.
According to the invention, the electronic control unit is arranged to generate control signals in order to initiate a free-wheeling mode. In response to these control signals, the first clutch unit is arranged to be deactivated, wherein the output shaft of the prime mover and the first input shaft are engaged. In the first transmission mechanism, each of the first set of gears connecting the first input shaft to the driving wheels are arranged to be disengaged. This is achieved by actuating relevant shift actuators in response to control signals generated by the electronic control unit.
At the same time, the second clutch unit is arranged to be deactivated, wherein the output shaft of the prime mover and the second input shaft are disengaged. In the second transmission mechanism, one of the second set of gears connecting the second input shaft to the driving wheels is arranged to be engaged. During a free-wheeling mode the second input shaft and the open second clutch will be rotated by means of the engaged gear and the driving wheels.
As described above, the first clutch unit is normally closed which means that the clutch is held in a closed, engaged position by a resilient means, a spring or a similar suitable means. To disengage the first clutch it is actuated by hydraulic pressure or other suitable means. The second clutch unit is normally open which means that the clutch is held in an open, disengaged position by a resilient means, a spring or a similar suitable means. To engage the second clutch it is actuated by hydraulic pressure or other suitable means.
During a free-wheeling mode a transmission lubricating device is drivingly connected to the first transmission mechanism. As indicated above, this arrangement ensures sufficient lubrication of the transmission during free-wheeling, when no torque is transmitted between the prime mover and the driving wheels.
When the control unit monitoring the dual clutch transmission detects input signals from the driver and/or the prime mover and transmission indicating that the free-wheeling mode should be exited, then the transmission is controlled to reconnect the prime mover and the driving wheels. According to the invention, a rapid reconnection of the prime mover to the driven wheels is achieved by engaging the second, normally open clutch unit. Prior to engagement, the control unit can select a suitable gear depending on the input signals from the driver and/or the prime mover. As none of the first set of gears connecting the first input shaft to the driving wheels in the first transmission mechanism is engaged, the first clutch unit can be disengaged during or after engagement of the second clutch unit.
The present invention also relates to a computer program, computer program product and a storage medium for a computer all to be used with a computer for executing the method as described in any one of the above examples.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.